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January 15, 2008

Black Holes Spin Near Speed of Light

by Sam Savage

Supermassive
black holes spin at speeds approaching the speed of light, new research
suggests.

Nine huge
galaxies were found to contain furiously whirling black holes that pump out
energetic jets of gas into the surrounding environment, according to a study
using data from NASA's Chandra X-ray Observatory.

"We
think these monster black holes are spinning close to the limit set by
Einstein's theory of relativity, which means that they can drag material around
them at close to the speed of light," said Rodrigo Nemmen, the study's lead
author and a visiting graduate student at Penn State University.

Einstein's
theory suggests spinning
black holes would make space itself rotate. The overall effect makes gas
spiral in toward the black hole, and also creates a magnetic field that shoots
inflowing gas back out as a jet.

Researchers
previously found that the greater the amount of gas falling into supermassive
black holes — known as the accretion rate — the greater the energy of the jets
shooting out. Leading theories suggest that the same jets drive the rotation of
the central black holes in galaxies.

"By
comparing observations of massive elliptical galaxies with current theories of
jet formation, we are able to get the spin of supermassive black holes,"
Nemmen told SPACE.com, explaining how his group ran computer simulations
and compared the results with Chandra's observations of the nine objects.

Black holes
can't be seen, but their existence and mass are inferred by their gravitational
effects on material around them and by the energy released from all the
activity.

The
observed jet power and accretion rates were huge — one black hole ate 10 Earth
masses per month and, from its surroundings, spat out 50 times the annual
energy of our sun per second. That allowed Nemmen and his colleagues to
estimate that the spin of the black holes approaches Einstein's speed-of-light
limit.

"Extremely
fast spin might be very common for large black holes," said
co-investigator Richard Bower of Durham University. "This might help us
explain the source of these incredible jets that we see stretching for enormous
distances across space."

The jets
produced by such high-speed spins heat the surrounding gaseous atmosphere and
can help trigger the birth of stars. However, such powerful jets could also destroy
the atmospheres of neighboring planets.

The new
research was detailed in a paper presented at a meeting of the American
Astronomical Society in Austin, Texas, last week.